Robust 24±6 ka 40Ar/39 Ar Age of a Low-Potassium Tholeiitic Basalt in the Lassen Region of NE California

2007 ◽  
Vol 68 (1) ◽  
pp. 96-110 ◽  
Author(s):  
Brent D. Turrin ◽  
L.J. Patrick Muffler ◽  
Michael A. Clynne ◽  
Duane E. Champion
Keyword(s):  
Basaltic Andesite ◽  
Tholeiitic Basalt ◽  
Lava Flows ◽  
Firm Age ◽  
Low Potassium ◽  
Total Fusion ◽  
Low K ◽  
Additional Constraints ◽  
Andesite Lava

Abstract40Ar/39Ar ages on the Hat Creek Basalt (HCB) and stratigraphically related lava flows show that latest Pleistocene tholeiitic basalt with very low K2O can be dated reliably. The HCB underlies ∼ 15 ka glacial gravel and overlies four andesite and basaltic andesite lava flows that yield 40Ar/39Ar ages of 38±7 ka (Cinder Butte; 1.65% K2O), 46±7 ka (Sugarloaf Peak; 1.85% K2O), 67±4 ka (Little Potato Butte; 1.42% K2O) and 77±11 ka (Potato Butte; 1.62% K2O). Given these firm age brackets, we then dated the HCB directly. One sample (0.19% K2O) clearly failed the criteria for plateau-age interpretation, but the inverse isochron age of 26"6 ka is seductively appealing. A second sample (0.17% K2O) yielded concordant plateau, integrated (total fusion), and inverse isochron ages of 26±18, 30±20 and 24±6 ka, all within the time bracket determined by stratigraphic relations; the inverse isochron age of 24"6 ka is preferred. As with all isotopically determined ages, confidence in the results is significantly enhanced when additional constraints imposed by other isotopic ages within a stratigraphic context are taken into account.

scholarly journals Studies on the glaciovolcanic and magmatic evolution of Ruapehu Volcano, New Zealand

2021 ◽  
Author(s):  
◽  
Christopher Edward Conway
Keyword(s):  
High Resolution ◽  
Trace Element ◽  
Basaltic Andesite ◽  
Incompatible Element ◽  
Melt Inclusions ◽  
Lava Flows ◽  
Glacial Retreat ◽  
High K ◽  
Low K

<p>This thesis undertakes a detailed case study of the processes and timescales of arc andesite-dacite magma generation and lava flow emplacement at a continental composite volcano. This has been achieved through the collection and integration of high-resolution field, geochronological and geochemical datasets for lava flows that form the edifice of Ruapehu.  The influence of syn-eruptive lava-ice interaction on the distribution and preservation of lava flows on glaciated composite volcanoes is investigated by characterising the morphology and fracture characteristics of effusive products at Ruapehu. Ice-bounded and ice-dammed lava flows display over-thickened (50–100 m-high) margins adjacent to or within glaciated valleys, are intercalated with till and have lateral margins that are pervasively fractured by quench-contraction cooling joints. These characteristics can be accounted for by impoundment and chilling of lava flows that were emplaced against large flank glaciers. In contrast, lava flows located within valleys have minimal moraine cover and glacial striae and are characterised by fracture networks indicative of only localised and minor interaction with ice/snow. These lavas were emplaced onto a relatively ice-free edifice following glacial retreat since ~18 ka.  New high-precision ⁴⁰Ar/³⁹Ar eruption ages and whole-rock major element geochemistry for lava flows are interpreted in the context of geologic mapping, volcano-ice interaction processes and previous chronostratigraphic studies. This provides a high-resolution eruptive history and edifice evolution model for Ruapehu. Sub-glacial to ice-marginal effusive eruption of basaltic-andesite and andesite constructed the northern portion of the exposed edifice between ~200 and 150 ka (Te Herenga Formation) and the wide southeastern planèze as well as parts of the northern, eastern and western flanks of Ruapehu between ~166 and 80 ka (Wahianoa Formation). No ages were returned for lava flows for the period from 80–50 ka, indicating one or a combination of: an eruptive hiatus; subsequent erosion and burial of lavas; or syn-eruptive glacial conveyance of lava flows to the ring-plain. The greater part of the modern edifice was constructed via effusion of lava flows of the syn-glacial Mangawhero Formation (50–15 ka) and post-glacial Whakapapa Formation (<15 ka). Syn-glacial edifice growth occurred primarily via effusion of andesite-dacite lava flows that formed ice-bounded ridges adjacent to valleyfilling glaciers. Post-glacial summit cones were constructed in the presence of remnant upper flank glaciers between 15 and 10 ka. Debuttressing of two northern summit cones and a southern summit cone as ice underwent continued post-glacial retreat resulted in two major Holocene sector collapses and deposition of debris avalanche deposits on the northern and south-eastern flanks of Ruapehu, respectively. The northern collapse scar was infilled by a new cone comprising <10 ka lava flows that form the modern upper northern and eastern flanks of the volcano. Late Holocene to historic eruptive activity has occurred through Crater Lake, which occupies the site of the collapsed southern cone.  New whole-rock major and trace element compositions for lavas and their mineral and melt inclusion geochemical characteristics are evaluated within the context of the improved chronostratigraphic framework. The new constraints are combined with existing whole-rock isotopic data to establish the long-term development of the magma generation system beneath Ruapehu. Basaltic-andesite lavas erupted between ~200 and 150 ka contain low-K₂O (2–3 wt. %) melt inclusions and have whole-rock compositions characterised by low incompatible element (K, Rb, Ba, Th, U) abundances and high ¹⁴³Nd/¹⁴⁴Nd-low ⁸⁷Sr/⁸⁶Sr when compared to younger eruptive products. In particular, basaltic-andesite to dacite lavas that were erupted between 50–35 ka define a high-K/Ca trend over a range of ~8 wt. % SiO₂ as well as elevated incompatible trace element contents when compared to all other documented eruptive products from Ruapehu. Rhyodacitic to rhyolitic melt inclusions, interstitial glass and melt pockets in partially fused feldspathic xenoliths contained within the dacite lavas from this latter period contain high K₂O (5–6 wt. %) and Rb contents (250–280 ppm). The whole-rock and glass characteristics of 50–35 ka lavas reflect the generation and assimilation of partial melts of the greywacke-argillite basement within the magma system beneath Ruapehu during this period. Selective partial melting and assimilation of fertile, K- and Rb-rich mineral phases (e.g. biotite) within the meta-sedimentary mineral assemblage is inferred to explain the enriched nature of these melts. A reversion to progressively less silicic and less potassic lavas with lower incompatible element abundances erupted since 26 ka is matched by the recurrent incorporation of crystals that trapped low-K₂O melt inclusions. The trend is interpreted to reflect the exhaustion of fertile phases within assimilated continental source rocks as the crust was progressively heated during long-term thermal conditioning of the arc lithosphere beneath Ruapehu.</p>

scholarly journals Studies on the glaciovolcanic and magmatic evolution of Ruapehu Volcano, New Zealand

2021 ◽  
Author(s):  
◽  
Christopher Edward Conway
Keyword(s):  
High Resolution ◽  
Trace Element ◽  
Basaltic Andesite ◽  
Incompatible Element ◽  
Melt Inclusions ◽  
Lava Flows ◽  
Glacial Retreat ◽  
High K ◽  
Low K

<p>This thesis undertakes a detailed case study of the processes and timescales of arc andesite-dacite magma generation and lava flow emplacement at a continental composite volcano. This has been achieved through the collection and integration of high-resolution field, geochronological and geochemical datasets for lava flows that form the edifice of Ruapehu.  The influence of syn-eruptive lava-ice interaction on the distribution and preservation of lava flows on glaciated composite volcanoes is investigated by characterising the morphology and fracture characteristics of effusive products at Ruapehu. Ice-bounded and ice-dammed lava flows display over-thickened (50–100 m-high) margins adjacent to or within glaciated valleys, are intercalated with till and have lateral margins that are pervasively fractured by quench-contraction cooling joints. These characteristics can be accounted for by impoundment and chilling of lava flows that were emplaced against large flank glaciers. In contrast, lava flows located within valleys have minimal moraine cover and glacial striae and are characterised by fracture networks indicative of only localised and minor interaction with ice/snow. These lavas were emplaced onto a relatively ice-free edifice following glacial retreat since ~18 ka.  New high-precision ⁴⁰Ar/³⁹Ar eruption ages and whole-rock major element geochemistry for lava flows are interpreted in the context of geologic mapping, volcano-ice interaction processes and previous chronostratigraphic studies. This provides a high-resolution eruptive history and edifice evolution model for Ruapehu. Sub-glacial to ice-marginal effusive eruption of basaltic-andesite and andesite constructed the northern portion of the exposed edifice between ~200 and 150 ka (Te Herenga Formation) and the wide southeastern planèze as well as parts of the northern, eastern and western flanks of Ruapehu between ~166 and 80 ka (Wahianoa Formation). No ages were returned for lava flows for the period from 80–50 ka, indicating one or a combination of: an eruptive hiatus; subsequent erosion and burial of lavas; or syn-eruptive glacial conveyance of lava flows to the ring-plain. The greater part of the modern edifice was constructed via effusion of lava flows of the syn-glacial Mangawhero Formation (50–15 ka) and post-glacial Whakapapa Formation (<15 ka). Syn-glacial edifice growth occurred primarily via effusion of andesite-dacite lava flows that formed ice-bounded ridges adjacent to valleyfilling glaciers. Post-glacial summit cones were constructed in the presence of remnant upper flank glaciers between 15 and 10 ka. Debuttressing of two northern summit cones and a southern summit cone as ice underwent continued post-glacial retreat resulted in two major Holocene sector collapses and deposition of debris avalanche deposits on the northern and south-eastern flanks of Ruapehu, respectively. The northern collapse scar was infilled by a new cone comprising <10 ka lava flows that form the modern upper northern and eastern flanks of the volcano. Late Holocene to historic eruptive activity has occurred through Crater Lake, which occupies the site of the collapsed southern cone.  New whole-rock major and trace element compositions for lavas and their mineral and melt inclusion geochemical characteristics are evaluated within the context of the improved chronostratigraphic framework. The new constraints are combined with existing whole-rock isotopic data to establish the long-term development of the magma generation system beneath Ruapehu. Basaltic-andesite lavas erupted between ~200 and 150 ka contain low-K₂O (2–3 wt. %) melt inclusions and have whole-rock compositions characterised by low incompatible element (K, Rb, Ba, Th, U) abundances and high ¹⁴³Nd/¹⁴⁴Nd-low ⁸⁷Sr/⁸⁶Sr when compared to younger eruptive products. In particular, basaltic-andesite to dacite lavas that were erupted between 50–35 ka define a high-K/Ca trend over a range of ~8 wt. % SiO₂ as well as elevated incompatible trace element contents when compared to all other documented eruptive products from Ruapehu. Rhyodacitic to rhyolitic melt inclusions, interstitial glass and melt pockets in partially fused feldspathic xenoliths contained within the dacite lavas from this latter period contain high K₂O (5–6 wt. %) and Rb contents (250–280 ppm). The whole-rock and glass characteristics of 50–35 ka lavas reflect the generation and assimilation of partial melts of the greywacke-argillite basement within the magma system beneath Ruapehu during this period. Selective partial melting and assimilation of fertile, K- and Rb-rich mineral phases (e.g. biotite) within the meta-sedimentary mineral assemblage is inferred to explain the enriched nature of these melts. A reversion to progressively less silicic and less potassic lavas with lower incompatible element abundances erupted since 26 ka is matched by the recurrent incorporation of crystals that trapped low-K₂O melt inclusions. The trend is interpreted to reflect the exhaustion of fertile phases within assimilated continental source rocks as the crust was progressively heated during long-term thermal conditioning of the arc lithosphere beneath Ruapehu.</p>

Effect of low-potassium diet on rat exercise hyperthermia and heatstroke mortality

1981 ◽  
Vol 51 (1) ◽  
pp. 8-13 ◽  
Author(s):  
R. W. Hubbard ◽  
M. Mager ◽  
W. D. Bowers ◽  
I. Leav ◽  
G. Angoff ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Body Weight ◽  
Plasma Potassium ◽  
Heat Illness ◽  
Sprague Dawley ◽  
Heat Gain ◽  
Sprague Dawley Rats ◽  
Low Potassium ◽  
Work Done ◽  
Low K

A total of 182 male Sprague-Dawley rats weighing 250–300 g were fed either a control (n = 122) diet for 32 days. The diets contained either 125 or 8 meq potassium/kg, respectively. Rats fed the low-K diet gained weight at only one-third the rate of controls (1.7 vs. 5.2 g/day), and their skeletal muscle and plasma potassium levels were reduced by 28 and 47%, respectively. When run to exhaustion at either 15 or 20 degrees C, low K+-fed rats accomplished less than one-half of the work done by the controls (26 vs. 53 kg. m) but exhibited a markedly greater rate of heat gain per kilogram-meter of work than controls (0.12 vs. 0.05 degrees C)ambient temperature of 20 degrees C, the rats of the low-K+ group despite large differences in body weight (-25%), run time temperature and twice (33 vs 17%) the mortality rate of the controls. Postexercise increases in circulating potassium (less than 90%) of heat-injured rats raised the plasma levels of low K+-fed rats to normal (5.9 +/- 2.2 meq/l). These results appear to characterize the existence of an insidious and, therefore, undocumented form of fatal exertion-induced heat illness.

Petrology and geochronology of Vran Kamak paleovolcano, Central Srednogorie, Bulgaria

2020 ◽  
Author(s):  
Stoyan Georgiev ◽  
Eleonora Balkanska ◽  
Irena Peytcheva ◽  
Dian Vangelov
Keyword(s):  
Lava Flow ◽  
Late Cretaceous ◽  
Basaltic Andesite ◽  
Upper Cretaceous ◽  
Small Degree ◽  
Lava Flows ◽  
Oscillatory Zoning ◽  
Primitive Mantle ◽  
Ministry Of Education ◽  
Igneous Activity

&lt;p&gt;Vran Kamak paleovolcano is formed during the Upper Cretaceous igneous activity along the Panagyurishte strip of Central Srednogorie Zone, Bulgaria, part of the magmatic-metalogenic arc belt Apuseni-Banat-Timok-Srednogorie. It represents a comparatively well-preserved, eroded stratovolcano built of epiclastics, pyroclastics and lava flow (with typical hyaloclastite and peperite formation) succession surrounded by marine environment, as only a part from the volcanic cone was over the sea level. The central (conduit) parts of the paleovolcano are intruded by a volcanic neck in the area of Vran Kamak summit. The volcanic activity was accompanied by sedimentary gravity flows and volcaniclastic debris is dispersed in the Late Cretaceous basin. The present study provides new petrological and geochronological data for Vran Kamak paleovolcano.&lt;/p&gt;&lt;p&gt;The analyzed samples from the lava flows show basaltic andesite to andesite composition with SiO&lt;sub&gt;2&lt;/sub&gt; contents ranging from 51 to 55.5 wt %, while the volcanic neck of the Vran Kamak summit is trachydacite (SiO&lt;sub&gt;2&lt;/sub&gt; of 61.54 wt % ). The rocks are medium- to high-K calc-alkaline. On a primitive-mantle normalized diagram, the rocks show peaks in LILE (U, Th, Pb) and troughs in Nb, Ta, Ti and P. Weak negative Eu anomaly (0.83&amp;#8211;0.94) and La&lt;sub&gt;N&lt;/sub&gt;/Yb&lt;sub&gt;N&lt;/sub&gt; (10 to 13) are observed. Fractionation of mafic minerals (amphibole and pyroxene) and plagioclase is visible on the harker diagrams. The &lt;sup&gt;87&lt;/sup&gt;Sr/&lt;sup&gt;86&lt;/sup&gt;Sr&lt;sub&gt;(i)&lt;/sub&gt; ratio of 0.705141 from the volcanic neck shows small degree of crustal assimilation.&lt;/p&gt;&lt;p&gt;The basaltic andesite to andesite lava flows are built of plagioclase (with normal oscillatory zoning, bytownite-labrador, An&lt;sub&gt;88-56&lt;/sub&gt;), amphibole (tschermakite to magnesiohastingsite) and pyroxenes (mostly augite and rare small enstatite crystals embedded in them). Some of the clinopyroxenes form corona texture around the amphibole, showing processes of dewatering. The trachydacite neck is built of porphyries of plagioclase, sanidine, biotite, amphibole (megnesiohornblende to thermakite), magmatically coroded quartz and accessories of zircon, apatite and magnetite set in a fine-grained groundmass. The calculated depths of crystallization and temperatures of the hornblende from the lava flows are 17&amp;#8211;22 km and 930&amp;#8211;970&lt;sup&gt; o&lt;/sup&gt;C and that from the neck are 5.9&amp;#8211;7 km and 800&amp;#8211;830 &lt;sup&gt;o&lt;/sup&gt;C, that give evidence for a complex volcano-plutonic system.&lt;/p&gt;&lt;p&gt;An attempt for LA-ICPMS U-Pb zircon dating of one the lava flows is made, but it contains only xenocrysts which fall in several age intervals: 306&amp;#8211;314 Ma, 440&amp;#8211;450 Ma, 520&amp;#8211;530 Ma, 560&amp;#8211;614 Ma, 810&amp;#8211;830 Ma which represent inherited and recycled component from the local basement. This lava flow has a peperitic contact with sediments faunistically dated at the Turonian/Coniacian boundary (Cremnoceramus deformis erectus, Vangelov et al., 2019). The zircon population of the trachydacite neck is presented mostly by own magmatic grown crystals giving a Concordia age of 91.12 &amp;#177;0.43 Ma.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Acknowledgements&lt;/strong&gt;. The study is supported by grant DN 04/9 funded by the National Science Fund, Ministry of Education and Science, Bulgaria.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References:&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Vangelov, D., Gerdjikov, I., Dochev, D., Dotseva, Z., Velev, S., Dinev, Y., Trayanova, D., Dancheva, J. 2019. Upper Cretaceous lithostratigraphy of the Panagyurishte strip (Central Bulgaria) &amp;#8211; part of the Late Cretaceous Apuseni-Banat-Timok-Srednogorie magmatic belt. &amp;#8211; Geol Balc., 48, 3, 11&amp;#8211;33.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

scholarly journals Crystal Forensics of Historical Lava Flows  from Mt Ngauruhoe

2021 ◽  
Author(s):  
◽  
Sophie Jan Barton
Keyword(s):  
New Zealand ◽  
Trace Element ◽  
Basaltic Andesite ◽  
Melt Inclusions ◽  
Lava Flows ◽  
Large Variability ◽  
Trace Element Chemistry ◽  
Element Chemistry ◽  
Mineral Zoning ◽  
Textural Evidence

<p>Mt Ngauruhoe is a 900 m high andesitic cone constructed over the last 2500 yr, and is the youngest cone of the Tongariro Massif. It was previously one of the most continuously active volcanoes in New Zealand, with ash eruptions having occurred every few years since written records for the volcano began in 1839. However, it has now been more than 30 yr since the last eruption. Eruptions in 1870, 1949, 1954 and 1974-1975 were accompanied by lava and block-and-ash flows. Detailed sampling of these historical lava and block-and-ash flows was conducted, including sampling from seven different lava flows erupted over the period June-September 1954 to investigate changes in magma geochemistry and crystal populations over short timescales, and to enable observed changes to be related back to known eruption dates. Mineral major and trace element chemistry highlights the importance of mixing between distinct basaltic and dacitic melts to generate the basaltic andesite whole rock compositions erupted. The basaltic end member can be identified from the presence of olivine crystals with Mg# 75-87, clinopyroxene cores with Mg# 82-92, and plagioclase cores of An80-90. The dacitic melt is identified by SiO2-rich clinopyroxene melt inclusions, clinopyroxene zoning with Mg# 68-76 and plagioclase rims of An60-70. Textural evidence from complex mineral zoning and large variability in the widths of reaction rims on olivine crystals suggests that mafic recharge of the more evolved system is frequent, and modelling of Fe-Mg inter-diffusion applied to the outermost rims of the clinopyroxene crystal population indicates that such recharge events have occurred weeks to months or even shorter prior to each of the historical eruptions, and thus likely trigger the eruptions.</p>

scholarly journals Root K affinity drivers and photosynthetic characteristics in response to low potassium stress in K high-efficiency vegetable soybean

2021 ◽  
Author(s):  
Changkai Liu ◽  
Xue Wang ◽  
Bingjie Tu ◽  
Yansheng Li ◽  
Heng Chen ◽  
...  
Keyword(s):  
Root Length ◽  
High Efficiency ◽  
Photosynthetic Parameters ◽  
Vegetable Soybean ◽  
Chl A ◽  
Low Potassium ◽  
Soybean Genotypes ◽  
Low Efficiency ◽  
Compensation Concentration ◽  
Low K

Abstract Aims Vegetable soybean is highly demanded on potassium (K) application. Significant variations of K absorption and utilization exist in vegetable soybean. This study aim at exploring mechanisms of K absorption and utilization of high-efficiency in vegetable soybean by studying the characteristics of root K affinity-associated drivers and photosynthesis in vegetable soybean (edamame) (Glycine max (L.) Merr.).Methods Pot and hydroponic experiments were carried out to examine the characteristics of root K affinity-associated drivers and photosynthesis in vegetable soybean genotypes with different K efficiency. Two K high-efficiency vegetable soybean genotypes and two K low-efficiency genotypes were investigated in low K and normal K conditions. Results The root of K high-efficiency genotypes had a higher K+ affinity associated with higher maximum K+ uptake rate (Imax), but lower Michaelis constant for K+ absorption (Km) and lower compensation concentration for K+ uptake (Cmin). Seedlings of K high-efficiency genotypes also had higher root vigor (TTC reduction method) and greater absorbing activity (methylene blue method), especially in the low K condition. Besides, the root bleeding-sap rate per root length and K upward fluxes rate per root length of K high-efficiency genotypes in beginning seed stage were consistently higher than that of K low-efficiency genotypes. The root of K high-efficiency vegetable soybean genotypes exhibits K+ high-affinity and driving advantages. Photosynthetic parameters of K high-efficiency vegetable soybean genotypes were less affected by low K stress. Low K stress decreased the net photosynthetic rate of K high-efficiency genotypes by 6.1~6.9%, while that of K low-efficiency genotypes decreased by 10.9~15.7%. The higher Chl a/b ratio with enhanced relative content of Chl a in response to low K stress might be an adapted mechanism for K high-efficiency genotypes to maintain photosynthetic capacity.Conclusion Stronger root K affinity drivers associated with photosynthetic adaptability to low potassium stress are the key factors in determining the K high-efficiency of vegetable soybeans.

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